Semiconductor Devices and Methods of Manufacture Thereof

ABSTRACT

Semiconductor devices and methods of manufacture thereof are disclosed. In a preferred embodiment, a method of manufacturing a semiconductor device includes forming a transistor, the transistor including a fin having a first side and a second side opposite the first side. The transistor includes a first gate electrode disposed on the first side of the fin and a second gate electrode disposed on the second side of the fin. The method includes forming a silicide or germanide of a metal on the first gate electrode and the second gate electrode of the transistor. The amount of the metal of the silicide or germanide is substantially homogeneous over the first gate electrode and the second gate electrode proximate the fin.

This is a divisional application of U.S. patent application Ser. No.11/810,858, entitled “Semiconductor Devices and Methods of ManufactureThereof” which was filed on Jun. 7, 2007 and is hereby incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates generally to semiconductor devices, andmore particularly to transistors having multiple gates and methods ofmanufacture thereof.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductive layers of material over asemiconductor substrate, and patterning the various layers usinglithography to form circuit components and elements thereon.

A transistor is an element that is utilized extensively in semiconductordevices. There may be millions of transistors on a single integratedcircuit (IC), for example. A common type of transistor used insemiconductor device fabrication is a metal oxide semiconductor fieldeffect transistor (MOSFET). Conventional MOSFETs have one gate electrodethat controls a channel region, and are often referred to as single gatetransistors. Early MOSFET processes used one type of doping to createsingle transistors that comprised either positive or negative channeltransistors. Other more recent designs, referred to as complementary MOS(CMOS) devices, use both positive and negative channel devices, e.g., apositive channel metal oxide semiconductor (PMOS) transistor and anegative channel metal oxide semiconductor (NMOS) transistor, incomplementary configurations.

Conventional bulk single-gate planar MOSFET devices are typically formedusing a three-dimensional doping profile, which includes channelimplantation, source and drain region implantation, lightly doped drain(LDD) extension implantation, and pocket/halo implantation processes.Scaling down bulk devices in size has limitations, because of anincrease in dopant fluctuations and stronger parasitic short channeleffects, due to lack of potential control in the channel region and thedeep substrate. Therefore, transistors with multiple gates are underdevelopment, such as vertical multiple-gate fin field effect transistors(FinFETs) or tri-gate devices.

A double gate transistor has two parallel gates that face each other andcontrol the same channel region. A FinFET is a vertical double gatedevice, wherein the channel comprises a vertical fin comprising asemiconductor material, typically formed on a silicon-on-insulator (SOI)substrate. The two gates of a FinFET are formed on opposing sidewalls ofthe vertical fin with an insulating material or hard mask formed on thetop of the fin.

FinFETs may be used to form CMOS devices. One or more FinFETs can beused as a PMOS and/or NMOS transistor: often, two or more fins inparallel are used to form a single PMOS or NMOS transistor, for example.FinFETs can be scaled more aggressively than planar transistorstructures, and show lower gate-induced drain leakage (GIDL) currentthan planar transistors. However, multiple gate transistors such asFinFETs are more difficult and complicated to manufacture than planarCMOS devices, and they require distinctly different materials andintroduce a variety of processing challenges.

Furthermore, it is important to design CMOS devices so that a symmetricthreshold voltage (V_(t)) for the NMOS and PMOS transistors of the CMOSdevice is achieved. However, it is difficult to find materials, devicestructures, and manufacturing processes that achieve a symmetricthreshold voltage V_(t) as devices are made smaller, and moreparticularly for advanced transistor designs having multiple gates.

Thus, what are needed in the art are improved structures andmanufacturing processes for multiple gate transistors.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention, which comprise novel structures and methods offorming gate electrodes of multiple gate transistors.

In accordance with a preferred embodiment of the present invention, amethod of manufacturing a semiconductor device includes forming atransistor, the transistor including a fin having a first side and asecond side opposite the first side. The transistor includes a firstgate electrode disposed on the first side of the fin and a second gateelectrode disposed on the second side of the fin. The method includesforming a silicide or germanide of a metal on the first gate electrodeand the second gate electrode of the transistor. The amount of the metalof the silicide or germanide is substantially homogeneous over the firstgate electrode and the second gate electrode proximate the fin.

The foregoing has outlined rather broadly the features and technicaladvantages of embodiments of the present invention in order that thedetailed description of the invention that follows may be betterunderstood. Additional features and advantages of embodiments of theinvention will be described hereinafter, which form the subject of theclaims of the invention. It should be appreciated by those skilled inthe art that the conception and specific embodiments disclosed may bereadily utilized as a basis for modifying or designing other structures,such as capacitors or gated diodes, as examples, or other processes forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 5 show cross-sectional views of a semiconductor deviceat various stages of manufacturing, illustrating a method of forminggate electrodes of a FinFET device in accordance with a preferredembodiment of the present invention;

FIG. 6 shows a cross-sectional view of a method of forming gateelectrodes of a FinFET device in accordance with another embodiment ofthe present invention;

FIG. 7 shows a cross-sectional view of a CMOS device comprising aplurality of PMOS transistors and NMOS transistors formed from FinFETdevices manufactured in accordance with an embodiment of the presentinvention;

FIG. 8 shows a cross-sectional view of a FinFET device in accordancewith an embodiment of the present invention after the formation of uppermetallization and insulating layers over the FinFET device; and

FIG. 9 shows a fin structure of the FinFET device shown in FIG. 8 in aview perpendicular to the view shown in FIG. 8.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

What are needed in the art are metal gate electrode materials andmethods of formation thereof that have a suitable work function formultiple gate CMOS devices. For CMOS FinFET technology to provide amaximum performance benefit over bulk-Si CMOS technology, one issue thatneeds to be resolved is the development of a tunable work function gatetechnology for threshold voltage V_(t) control.

Because a FinFET controls the channel region by two gates disposed onboth sides of a very thin fin of vertical silicon film, a FinFET devicerequires near mid-gap work functions rather than band-edge workfunctions, as in planar devices. An n channel FinFET requires a workfunction in a range from about 4.65 eV for low standby powerapplications to about 4.45 eV for high performance applications, asexamples. A p channel FinFET requires a work function in a range fromabout 4.65 eV for low standby power applications to about 4.85 eV forhigh performance applications, as examples. These work functions wouldresult in symmetrical voltage thresholds V_(tn) and V_(tp) (e.g.,V_(tn)=+0.3 V and V_(tp)=−0.3 V, although other voltage thresholds mayalso be used) for the n channel and p channel devices, which is requiredfor a CMOS device, for example.

One approach of establishing work functions and also to improveconductivity of gate electrode materials is to silicide the gatematerial, e.g., by depositing a metal over a polysilicon gate material,and heating the device, causing the metal to diffuse into and/or bondwith the polysilicon gate material. In some applications, it isdesirable to fully silicide (FUSI) the gate material, for example.However, there can be many phases of silicide that result from asilicidation process. For example, nickel silicide has six phases at lowtemperatures: Ni₃Si, Ni₃₁Si₁₂, Ni₂Si, Ni₃Si₂, NiSi, NiSi₂, with eachphase resulting in a different work function.

Siliciding of gate electrode materials of FinFETs is difficult becauseof the three-dimensional structures of the vertical fins used for thechannel region. The vertical fin has corners and edges, and when apolysilicon gate material is formed over the fin, the thickness of thegate material may vary over the fin. The fin structures result in adifferent amount of polysilicon residing on the surface at the top ofthe fin and at the bottom of the fin, which may react differently withthe silicidation metal, such as nickel, during the silicidation process.The amount of polysilicon gate material may have different filmthicknesses on horizontal services, vertical surfaces, at the edges, andat the corners of the fin, for example.

Different amounts of polysilicon gate material over the surface of thefin during the silicidation process causes different grain boundariesand different silicide phases across the surface of the fin. Thedifferent silicide phases result in different work functions at variouslocations around the fin. The varying work functions around the fincause a parasitic device behavior referred to as bi-modal V_(t), whichis undesirable and should be avoided. FinFETs exhibiting this problemmay have different threshold voltage V_(t) for the sidewalls and the topof the fin, e.g., leading to V_(t) splits within a single transistor ordevice, or resulting in V_(t) splits in adjacent devices on the samedie. Thus, controlling the V_(t) during silicidation of a FinFET can bechallenging, because the V_(t) may be split into two or more “modes,”depending on the silicidation process and the geometry of the structure,resulting in under-silicidation or over-silicidation of portions of thegate material over the fin.

For example, silicided edge and top, outer, corner regions of the finmay have excess metal or may be metal-rich, and silicided inner cornersnear the bottom of the fin may have less metal or may be metal-poor. IfNi is used as a silicidation metal, the top corners of the fin may formNi₂Si, and the lower inner corners near the bottom of the fin may formNiSi₂, as examples. Such variations in the silicide phase may result inunpredictable or unreliable device performance, decreased deviceperformance, and/or device failures in some applications, for example.

It is desirable to form a single stable phase of silicide over a surfaceof the fin when forming a partially or fully silicided (FUSI) gate on aFinFET. However, the process window to form a single stable NiSi phasesis relatively small, e.g., between 5 and 20 degrees Celsius, dependingon the processing options. Processing out of this process window mayalso lead to over-silicidation or under-silicidation of the polysilicongate material and may lead to different phases of silicide, e.g.,forming Ni_(x)Si_(y), wherein x and y have varying values across thesurface of the gate material.

Embodiments of the present invention achieve technical advantages byproviding processing solutions that solve the problem of geometrydependent V_(t) in FinFET devices. Several methods of solving theproblem will be described, which may be used alone or in combination toimprove the silicidation process and achieve a homogeneous phase ofsilicide over the channel region of the fin.

The present invention will be described with respect to preferredembodiments in a specific context, namely in CMOS FinFET devices.Embodiments of the present invention may also be applied, however, toother semiconductor device applications where transistors having two ormore gate electrodes are utilized. The terms “gate” and “gate electrode”refer to the gate of a transistor, and these terms are usedinterchangeably herein.

FIGS. 1 through 5 show cross-sectional views of a semiconductor device100 at various stages of manufacturing, illustrating a method of forminggate electrodes of a FinFET device in accordance with a preferredembodiment of the present invention. Note that in the drawings, only twoFinFET devices 130 are shown; however, there may be many transistorsformed on a semiconductor workpiece 102 during each of the manufacturingprocesses described herein.

With reference first to FIG. 1, there is shown a semiconductor device100 in a cross-sectional view including a workpiece 102. The workpiece102 preferably comprises a semiconductor-on-insulator substrate. Theworkpiece 102 may comprise a silicon-on-insulator (SOI) substrate orgermanium-on-insulator (GOI) substrate, for example. The SOI substrateincludes a first layer of semiconductive material 104 that comprises asubstrate, a buried insulating layer 106 or buried oxide layer disposedover the first layer of semiconductive material 104, and a second layerof semiconductive material 108 disposed over the buried insulating layer106, for example. The workpiece 102 may also include other activecomponents or circuits formed in other regions of the workpiece 102, notshown. The workpiece 102 may comprise silicon oxide over single-crystalsilicon, for example. The workpiece 102 may include other conductivelayers or other semiconductor elements, e.g., transistors, diodes, etc.Compound semiconductors, GaAs, InP, Si/Ge, or SiC, as examples, may beused in place of silicon. The workpiece 102 may be doped with P typedopants and N type dopants, e.g., to form P wells and N wells,respectively (not shown). The second layer of semiconductor material 108may comprise silicon (Si) having a thickness of about 100 nm, forexample, although alternatively, the second layer of semiconductormaterial 108 may comprise other materials and dimensions. The buriedinsulating layer 106 may comprise a thickness of about 150 nm, forexample, although the buried insulating layer 106 may alternativelycomprise other dimensions.

A hard mask 110/112/114 is formed over the workpiece 102. The hard mask110/112/114 may comprise a single layer of material or a plurality ofmaterial layers. The hard mask 110/112/114 preferably comprises an oxidelayer, a nitride layer, or combinations or multiple layers thereof, forexample. The hard mask 110/112/114 preferably comprises a thickness ordimension d₁ of greater than about 50 nm in some embodiments, forexample, although alternatively, the hard mask 110/112/114 may compriseother dimensions. The thickness d₁ of the hard mask 110/112/114 is alsoreferred to herein as a first thickness, for example.

In some embodiments, the hard mask 110/112/114 preferably comprises atri-layer, as shown in FIG. 1. The hard mask 110/112/114 may comprise afirst oxide layer 110 comprising about 10 nm of SiO₂ formed over theworkpiece 102. A nitride layer 112 comprising about 20 nm of Si_(x)N_(y)is formed over the first oxide layer 110. A second oxide layer 114comprising about 20 nm of SiO₂ is formed over the nitride layer 112.Alternatively, the hard mask 110/112/114 may comprise other materialsand dimensions, for example.

The hard mask 110/112/114 is patterned using lithography, e.g., bydepositing a layer of photoresist (not shown) over the hard mask110/112/114, exposing the layer of photoresist to energy using alithography mask, developing the layer of photoresist, and using thelayer of photoresist as a mask to pattern the hard mask 110/112/114, forexample. The hard mask 110/112/114, and optionally, also the layer ofphotoresist are used as a mask to pattern at least the second layer ofsemiconductive material 108 of the workpiece 102, as shown in FIG. 2.The buried insulating layer 106 may comprise an etch stop layer for theetch process of the second layer of semiconductive material 108, forexample. A top portion of the buried insulating layer 106 may be removedduring the etch process of the second layer of semiconductive material108, as shown. For example, the buried insulating layer 106 may beetched by an amount d₁ comprising about 15 nm or less, althoughalternatively, d₁ may comprise other dimensions.

The patterned second layer of semiconductor material 108 forms verticalfins 108 of semiconductor material extending in a vertical directionaway from a horizontal surface of the workpiece 102. The fin structures108 will function as the channels of PMOS and NMOS FinFET devices, to bedescribed further herein. The fin structures 108 have a thickness d₂that may comprise about 50 nm or less, as an example, althoughalternatively, the fins 108 may comprise other dimensions. For example,the thickness d₂ of the fin structures 108 may comprise about 5 to 60nm, or less, in some applications. As another example, the thickness d₂of the fin structures 108 may be larger, such as having a thickness d₂of about 100 to 1,000 nm. The thickness d₂ of the fin structures 108 mayvary as a function of the channel doping and other dimensions of the finstructures 108, as examples, although other parameters may also have aneffect on the determination of the dimension d₂.

The fin structures 108 have a height equivalent to the thickness of thesecond layer of semiconductor material 108, for example. Only two finstructures 108 are shown in FIG. 2; however, there may be many finstructures 108, e.g., about 1 to 200 fin structures, for a PMOS or NMOSdevice, as examples, although alternatively, other numbers of finstructures 108 may be used.

A gate dielectric material 116 is formed over at least the sidewalls ofthe fins of semiconductor material 108, as shown in FIG. 2. The gatedielectric material 116 may be formed using a thermal oxidation process,for example, wherein only the semiconductor material 108 is oxidized(not shown in FIG. 2; see FIGS. 7 at 216 a and 216 b). Alternatively,the gate dielectric material 116 may be formed using a depositionprocess, resulting in a thin layer of the gate dielectric material 116also being formed on the buried insulating layer 106 and the hard mask110/112/114 as shown in FIG. 2, for example. The gate dielectricmaterial 116 preferably comprises a hafnium-based dielectric, HfO₂,HfSiO_(x), Al₂O₃, ZrO₂, ZrSiO_(x), Ta₂O₅, La₂O₃, HfAlO_(x), ZrAlO_(x),SiAlO_(x), HfSiAlO_(x), ZrSiAlO_(x), Y₂O₃, TiO₂, nitrides thereof,Si_(x)N_(y), SiON, SiO₂, or multiple layers or combinations thereof, asexamples, although alternatively, the gate dielectric material 116 maycomprise other materials.

The gate dielectric material 116 preferably comprises a high kdielectric material having a dielectric constant greater than thedielectric constant of SiO₂ in some embodiments. For example, the gatedielectric material 116 preferably comprises a high k dielectricmaterial having a dielectric constant of about 4.0 or greater, forexample. The gate dielectric material 116 preferably comprises athickness of about 50 Angstroms or less in one embodiment, althoughalternatively, the gate dielectric material 116 may comprise otherdimensions.

The gate dielectric material 116 may be formed by chemical vapordeposition (CVD), atomic layer deposition (ALD), physical vapordeposition (PVD), jet vapor deposition (JVD), an oxidation, and/or anitridation process, as examples, although alternatively, the gatedielectric material 116 may be formed using other suitable techniques.

Next, a gate electrode material 118 having a thickness d₃ is formed overthe fin structures 108, as shown in FIG. 3. The gate electrode material118 preferably comprises a semiconductive material, for example. Thegate electrode material 118 may comprise amorphous silicon, polysilicon,undoped silicon, doped silicon, or other semiconductor materials such asgermanium, as an example.

In accordance with a first embodiment of the present invention,advantageously, the gate electrode material 118 is deposited having athickness or dimension that is sufficiently thin to facilitate orimprove a subsequent silicidation process. The gate electrode material118 preferably comprises a thickness or dimension d₃ of about 50 nm orless, for example, although alternatively, the gate electrode material118 may comprise other dimensions. The gate electrode material 118preferably is thin enough to ensure that the gate electrode material 118is fully silicided during the subsequent silicidation process in someembodiments, for example. The gate electrode material 118 is preferablydeposited in a thickness that will maintain the relatively low aspectratio of the fin 108 height-to-width; e.g., which may comprise about 3:1or less, in some embodiments.

In some embodiments, the gate electrode material 118 is preferablythinner than the hard mask 110/112/114. For example, dimension d₃, thethickness of the gate electrode material 118, which is also referred toherein as a second thickness, is preferably less than the dimension d₁or first thickness of the hard mask 110/112/114 in some embodiments.

The gate electrode material 118 may be deposited using CVD, ALD, PVD, orJVD, as examples, although alternatively, the gate electrode material118 may be formed using other suitable techniques. The gate electrodematerial 118 comprises a first gate electrode on a first sidewall orside of a fin of semiconductor material 108. The gate electrode material118 comprises a second gate electrode on a second sidewall or side ofthe fin of semiconductor material 108 opposite the first sidewall orside. Thus, a dual gate electrode structure is formed on the fins ofsemiconductor material 108. Again, several fins 108 may be placed inparallel to form a PMOS or NMOS FinFET device, for example.

The hard mask 110/112/114 is preferably thicker than the first gateelectrode and the second gate electrode on the sides of the fin 108 insome embodiments, for example. The hard mask 110/112/114 preferablycomprises a greater thickness d₁ than the thickness d₃ of the first gateelectrode and the second gate electrode, for example.

Next, the gate electrode material 118 is silicided or germanided. Tosilicide or germanide the gate electrode material 118, a metal layer 120is formed over the gate electrode material 118, as shown in FIG. 4 in across-sectional view. The metal layer 120 may be formed using PVD, e.g.,by sputtering on the metal, although alternatively, other depositionmethods may be used. The workpiece 102 is then heated or annealed, e.g.,using a rapid thermal anneal (RTP) or other heat process, causing theatoms of the metal layer 120 to move downward into the gate electrodematerial 118 toward the gate dielectric material 116 and combine orchemically react with atoms of the gate electrode material 118. Themetal layer 120 preferably comprises Ni, Co, Ti, Pt, a rare earthelement such as Yb, Eu, La, Ce, Pr, Pm, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm,Ln, other metals, or combinations thereof, as examples, althoughalternatively, the metal layer 120 may comprise other materials. Themetal layer 120 preferably comprises a thickness of about 50 nm or less,although alternatively, the metal layer 120 may comprise otherdimensions.

The deposition process and the temperature, duration, and otherparameters of the anneal process are preferably selected to achieve adesired phase of silicide or germanide, for example. The metal layer 120is then removed, leaving behind gate electrode material 122 that issilicided or germanided, as shown in FIG. 5. If the metal layer 120comprises Ni, the silicided or germanided gate electrode material 122preferably comprises NiSi or Ni₃Si₂ in some embodiments, for example,although other phases of Ni_(x)Si_(y) and other silicides or germanidesmay also be formed.

The gate electrode material 118 and the silicidation or germanidationprocess are preferably selected to optimize the homogeneity of the phaseof the silicide or germanide 122 in some embodiments of the presentinvention, for example. The phase of the silicide or germanide 122formation may vary according to processing conditions, such as annealconditions, time, temperature, and other parameters, for example.

Either before or after the silicidation process, the gate electrodematerial 118 or silicided or germanided gate electrode material 122 maybe implanted with a dopant species, in some embodiments. The dopantspecies may comprise As, P, Sb, B, C, Ge, a rare earth element such asYb, Eu, La, Ce, Pr, Pm, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Ln, orcombinations thereof, although other elements may also be implanted intothe gate electrode material 118 or 122. If the metal layer 120 comprisesNi, for example, the silicided gate electrode material 122 may compriseNiSi or Ni₃Si₂ doped with P or B in some embodiments, although otherphases of Ni_(x)Si_(y) and other dopant species may also be used.

The manufacturing process for the semiconductor device 100 is thencontinued. For example, portions of the gate electrode material 122 maybe removed to form the gate electrodes for the CMOS FinFETs, e.g., thegate electrode material 122 and optional semiconductor material 124 aresimultaneously patterned to form the gate electrodes of the FinFETdevices, respectively. In some embodiments, the gate electrode material122 is preferably patterned before the deposition of the metal layer120, for example. Additional insulating material layers may be formedover the gate electrodes. Contacts may be made to the source, drain, andgate electrodes of the FinFETs, for example, as shown in FIGS. 8 and 9(to be described further herein).

Advantageously, FinFET devices 130 are formed that have an amount of themetal of the silicide or germanide, e.g., the silicided or germanidedgate electrode material 122, that is substantially homogeneous over thefirst gate electrode 122 and the second gate electrode 122 proximate thefins 108. The first gate electrode and a second gate electrodeadvantageously comprise a substantially homogeneous phase of silicide orgermanide over the entire fin 108 height, represented by region 124 inFIG. 5, of the fins 108. An amount of doping of the first and secondgate electrodes 122, a selection of the gate dielectric material 116,and/or the phase of the silicided or germanided gate electrode material122 may be selected and chosen to establish a desired, predeterminedvalue of the work function of the FinFET devices 130, in accordance withembodiments of the present invention, thus establishing the desiredthreshold voltage V_(t) of the FinFET devices 130, for example.

For example, to achieve a silicide having a phase of NiSi, thetemperature of the anneal process during silicidation is preferablyrelatively low, e.g., comprising a temperature of about 450 degrees C.To achieve a silicide having a phase of Ni₃Si₂, the temperature of theanneal process during silicidation is preferably relatively higher,e.g., comprising a temperature of about 520 degrees C. Alternatively,other temperatures may be used for the anneal process, for example.

Because in some embodiments, the gate electrode material 118/122 isthin, the silicidation process is improved, resulting in a fullysilicided or germanided gate electrode material 122 and increasing thelikelihood that a homogenous phase of the silicide or germanide willform over the entire length of the gate electrode material proximate thefin 108, e.g., the channel region, along the entire height of region124.

In other embodiments, because the hard mask 110/112/114 is thicker thanthe gate electrode material 118/122, the top corners and edges 126 ofthe gate electrode material 118/122 are raised upwardly away from theworkpiece 102, e.g., by an amount or dimension d₄, as shown in FIG. 5.Dimension d₄ is substantially equal to the thickness d₁ of the hard mask110/112/114 and the thickness d₃ of the gate electrode material 118/122,for example. Thus, if any inhomogeneities are formed in the phase of thesilicided or germanided gate electrode material 122 at the top cornerand edges 126, the phase inhomogeneities (e.g., such as metal-richphases of the silicide or germanide) are positioned farther away fromthe fins 108 comprising the channel region, and thus, the phaseinhomogeneities will not deleteriously affect device 130 performance,advantageously.

FIG. 6 shows a cross-sectional view of another method of forming gateelectrodes of a FinFET device 130 in accordance with another embodimentof the present invention Like numerals are used for the element numbersin FIG. 6 as were used in FIGS. 1 through 5, and similar materials andthicknesses are preferably used for the element numbers as werepreviously described for FIGS. 1 through 5.

In this embodiment, during the etch process to form the fins 108, theburied insulating layer 106 is preferably over-etched, as shown. Theburied insulating layer 106 is preferably recessed by an amountrepresented by dimension d₅ below a bottom surface of the secondsemiconductor material 108 of the workpiece 102, e.g., below the bottomsurface of the fins 108. The amount of the recess or dimension d₅ belowthe bottom surface of the fins 108 is preferably greater than thethickness of the gate electrode material 118/122, e.g., greater than thethickness of the first gate electrode and the second gate electrode 122formed from the gate electrode material 122 on the sides or sidewalls ofthe fins 108, as shown in FIG. 6. The recess or dimension d₅ ispreferably greater than about 50 nm in some embodiments, for example,although alternatively, the recess may comprise other dimensions.

Advantageously, if the inner corners 128 of the gate electrode materialare under-silicided or germanided, forming a metal-poor silicide orgermanide in the inner corners 128, the recessed buried insulating layer106 further distances any silicide or germanide phase inhomogeneitiesaway from the channel region, e.g., region 124 of the fins 108. Becausethe recess having dimension d₅ in the buried insulating material 106 isgreater than the thickness of the gate electrode material 118/122, theinner corners 128 of the gate electrode material 118/122 are lowereddownwardly away from the fins 108, e.g., by an amount or dimension d₆,as shown in FIG. 6. Dimension d₆ is substantially equal to the amount d₅of the recess less the thickness d₃ of the gate electrode material118/122, for example. Thus, if any inhomogeneities are formed in thephase of the silicided or germanided gate electrode material 122 at theinner corners 128, the silicide or germanide phase inhomogeneities(e.g., such as metal-poor phases of the silicide or germanide) arepositioned farther away from the fins 108 comprising the channel region(e.g., region 124 that comprises the active silicon regions of theFinFET device 130), and thus, the silicide or germanide phaseinhomogeneities will not deleteriously affect device 130 performance,advantageously.

Note that the embodiment shown in FIG. 6 is preferably combined with theembodiments shown in FIGS. 1 through 5, wherein the gate electrodematerial 118/122 preferably comprises a dimension d₃ sufficiently thinenough to facilitate the silicidation process, and wherein the hard mask110/112/114 is preferably thicker than the gate electrode material118/122. Advantageously, synergistic effects of combining the variousembodiments of the invention described herein may be achieved,optimizing the homogeneity of the silicide or germanide formationproximate the fins 108, particularly when the gate electrode material122 is fully silicided or germanided, for example. The work function andthreshold voltage may be tuned by the phase control of the silicide orgermanide 122 formation, achieving a homogeneous mid-gap work functionalong the height of the fins 108 proximate the channel region, accordingto embodiments of the present invention.

Alternatively, the embodiments described herein may be implemented alonein a semiconductor device 100, e.g., wherein the gate electrode material118/122 preferably comprises a dimension sufficiently thin enough tofacilitate the silicidation process, yet wherein the hard mask110/112/114 is not thicker than the gate electrode material 118/122, andwherein the buried insulating material 106 is not recessed Likewise, therecess in the buried insulating material 106 may be greater than thethickness of the gate electrode material 118/122, yet the hard mask110/112/114 may not be thicker than the gate electrode material 118/122,as another example. Other combinations of the various embodiments of thepresent invention described herein may also be used, for example.

In some embodiments, the silicided or germanided gate electrode material122 is preferably fully silicided or germanided. However, in otherembodiments, the silicided or germanided gate electrode material 122 maybe silicided or germanided only in a top region, e.g., in an outerregion of the gate electrode material 122, leaving the lower or innerregions of the gate electrode material 118 unsilicided or ungermanided.

Because silicide or germanide phase inhomogeneities of the gateelectrode material 122 proximate the fin 108 are reduced (or eliminated,if all embodiments of the present invention described herein arecombined) using embodiments of the invention described herein,advantageously, the threshold voltage of the FinFET device 130 issubstantially the same across an entire surface of the first gateelectrode and the second gate electrode 122, for example. Any silicideor germanide phase inhomogeneities, e.g., metal-rich or metal-poorphases are not formed close to the fins 108, and thus have no impact onthe device 130 effective work function or threshold voltage,advantageously.

The threshold voltage may be tuned by forming a selected, desired phaseof silicide or germanide, and/or the threshold voltage may be furthertuned by the selection of the gate dielectric material and/or by thedoping of the gate electrode material 122. For example, if the gateelectrode material 122 comprises nickel silicide, a gate dielectricmaterial 116 comprising SiO₂, HfSiO, or HfSiON may be used inconjunction with a selected phase of the Ni_(x)Si_(y) to achieve aparticular work function.

In some embodiments, e.g., if the silicide of the gate electrodematerial 122 comprises Ni_(x)Si_(y), the target nickel phase of thesilicide formed is preferably about 60 to 50%, for example.Alternatively, other targeted metal phases of the silicide or germanidemay also be used.

In some embodiments and applications, an NiSi₂ phase is preferablyavoided, for example. The NiSi₂ phase of nickel silicide has a muchgreater resistance than the NiSi phase, e.g., three times theresistance, as an example, and thus is less conductive than NiSi. Inother embodiments and applications, an Ni₂Si phase is preferablyavoided, due to the work function of this phase of silicide, which isaround 4.8, which may be unsuitable in certain applications. Likewise,other phases of silicide or germanide may be preferred or less preferredin certain applications, depending on the resistance, work function, andother parameters, as examples.

Some examples of work functions for multiple gate FETs that may beachieved in accordance with embodiments of the present invention areshown in Table 1, as examples. Alternatively, other types of silicidesor germanides and doping configurations may also be used.

TABLE 1 Transistor type Silicide and phase Doping Work function Lowstandby power n NiSi or Ni₃Si₂ Undoped 4.65 eV channel FinFET Highperformance n NiSi or Ni₃Si₂ P doped 4.45 eV channel FinFET Low standbypower p NiSi or Ni₃Si₂ Undoped 4.65 eV channel FinFET High performance pNiSi or Ni₃Si₂ B doped 4.85 eV channel FinFET

The work function for devices formed on a gate dielectric materialcomprising SiO₂ having an NiSi or Ni₃Si₂ phase are higher for B dopedgate electrode material (e.g., about 4.8 eV), whereas the same materialsdoped with P achieve a work function of about 4.5, for example. Undoped,these materials have a work function of about 4.6 to 4.7, for example.The work function for devices formed on a gate dielectric materialcomprising SiO₂ and having an Ni₂Si phase doped with P comprise a workfunction of about 4.7 eV, and doped with B comprise a work function ofabout 4.6 eV, for example. Thus, the work function may be tuned byadjusting the doping, silicide or germanide phase, and gate dielectricmaterial, in accordance with embodiments of the present invention, toachieve a desired threshold voltage for a FinFET device.

Advantageously, embodiments of the present invention provide methods offorming easily tunable mid-gap work function silicide or germanide gateelectrodes, which may be used in low standby power, high performance, orother applications. Embodiments of the present invention may beimplemented in logic devices, memory devices, peripheral circuitrydevices, or other applications, as examples.

FIG. 7 shows a cross-sectional view of a CMOS device 200 comprising aplurality of PMOS transistors 230 a and NMOS transistors 230 b formedfrom FinFET devices manufactured in accordance with an embodiment of thepresent invention. Again, like numerals are used for the variouselements that were described in FIGS. 1 through 6. To avoid repetition,each reference number shown in FIG. 7 is not described again in detailherein. Rather, similar materials x02, x04, x06, x08, etc. . . . arepreferably used for the various material layers shown as were describedfor FIGS. 1 through 6, where x=1 in FIGS. 1 through 6 and x=2 in FIG. 7.As an example, the preferred and alternative materials and dimensionsdescribed for the silicided or germanided gate electrode materials 122in the description for FIGS. 1 through 6 are preferably also used forthe silicided or germanided gate electrode materials 222 a and 222 b ofFIG. 7.

The semiconductor device 200 includes at least one first region 232wherein PMOS FinFETs 230 a will be formed, and at least one secondregion 234 wherein NMOS FinFETs 230 b will be formed, as shown. Only onefirst region 232 and one second region 234 are shown in the figures;however, there may be many first regions 232 and second regions 234formed on a semiconductor device 200, for example. The first region 232and the second region 234 may be separated by isolation regions (notshown in FIG. 7; see FIG. 9 at 352, for example).

The first region 232 may be masked while the second region 234 isprocessed. Likewise, the second region 234 may be masked while the firstregion 232 is processed. The silicided or germanided gate electrodematerials 222 a and 222 b may be silicided or germanided simultaneously,and the work function and threshold voltages may be tuned using otherparameters, such as doping levels and/or selection of the gatedielectric materials 216 a and 216 b, for example. Alternatively, thesilicided or germanided gate electrode material 222 a and 222 b may besilicided or germanided separately while the second region 234 or firstregion 232 are masked, and the silicide or germanide phase of thesilicided or germanided gate electrode materials 222 a and 222 b may beused as a parameter to tune the work function and threshold voltages ofthe FinFETs 230 a and 230 b, as another example. Note that in theembodiment shown in FIG. 7, the gate dielectric material 216 a and 216 bmay be formed by oxidizing the sidewalls of the fins 208 a and 208 b, sothat the gate dielectric materials 216 a and 216 b are not formed onother exposed surfaces. Alternatively, the gate dielectric materials 216a and 216 b may be formed on all exposed surfaces, as shown in FIGS. 1through 6.

Advantageously, each of the FinFET devices 230 a and 230 b comprise afirst gate electrode and a second gate electrode comprising gateelectrode materials 222 a and 222 b, respectively, that comprise asubstantially homogeneous phase of the silicide or germanide over theentire height of the fin, due to the thinness of the gate electrodematerials 222 a and 222 b, the thicker hard masks 210 a/212 a/214 a and210 b/212 b/214 b, recessed buried insulating material 206, and/or thefully silicided or germanided gate electrode materials 222 a and 222 b,in accordance with embodiments of the present invention. The phase ofthe silicide or germanide of the gate electrode materials 222 a and 222b may be the same phase or may comprise different phases, for example.

In some embodiments, the work function of the p channel transistors 230a in the first region 232 preferably comprises about 4.6 to 4.9 eV, andthe work function of the n channel transistors 230 b in the secondregion 234 preferably comprises about 4.4 to 4.7 eV. The work functionof the transistors 230 a and 230 b are preferably different in someembodiments, for example.

The transistors 230 a and 230 b in the first and second regions 232 and234 preferably comprise symmetric threshold voltages V_(t) in accordancewith some embodiments of the present invention, for example. Thetransistors 230 a and 230 b preferably have substantially symmetricthreshold voltages of about +0.3 and −0.3 V, respectively, as examples,in one embodiment, although the threshold voltages may alternativelycomprise other voltage levels, such symmetric V_(t) values of about+/−0.1 V to about 15 V, as examples.

FIG. 8 shows a cross-sectional view of a FinFET device 330 a inaccordance with an embodiment of the present invention after theformation of upper metallization and insulating layers over the FinFETdevice 330 a. FIG. 9 shows a fin structure of the FinFET device 330 ashown in FIG. 8 in a view perpendicular to the view shown in FIG. 8. TheFinFET gate electrode material 322 a preferably is formed using thenovel embodiments described herein, for example. Portions of the finstructures 308 a comprise channel regions 308 a ₁, and other portions ofthe fin structures 308 a may be implanted with dopants to form sourceregion 308 a ₂ and drain region 308 a ₃, as shown in FIG. 9. A view ofthe channel 308 a ₁ disposed between the source region 308 a ₂ and thedrain region 308 a ₃ can also be seen in the view shown in FIG. 9, forexample. The implantation steps to form the source and drain regions 308a ₂ and 308 a ₃ may alternatively take place before the manufacturingprocess steps described herein, in some embodiments, for example.Spacers 354 comprising an insulating material such as an oxide, nitride,or combinations thereof, may be formed over the sidewalls of the gateelectrodes 322 a and hard mask 310 a/312 a/314 a, also shown in FIG. 9.Insulating and conductive layers may be formed over the CMOS FinFET ortri-gate transistors, such as insulating layers 344 and 350 andconductive layers 346 a/346 b/346 c and 348 a/348 b/348 c. The gatedielectric material 310 a is shown disposed beneath the sidewall spacers354, which is optional; alternatively, the gate dielectric material 310a may not be disposed beneath the sidewall spacers 354 in someembodiments, for example.

Contact 346 a (FIG. 8) provides electrical contact to the gate of themultiple gate device, e.g., making contact with the gate electrodematerial 322 a Likewise, contact 346 b (FIG. 9) provides electricalcontact to the source 308 a ₂ via silicide or germanide 342 formed overthe source 308 a ₂, and contact 346 c provides electrical contact to thedrain 308 a ₃ via silicide or germanide 342 formed over the drain 308 a₃.

Additional metallization and insulating layers may be formed andpatterned over the top surface of the insulating material and contacts,such as conductive lines 348 a, 348 b, and 348 c that make electricalcontact to the contacts 346 a, 346 b, and 346 c. Bond pads (not shown)may be formed over contacts, and a plurality of the semiconductordevices 300 may then be singulated or separated into individual die. Thebond pads may be connected to leads of an integrated circuit package(also not shown) or other die, for example, in order to provideelectrical contact to the multiple gate transistors 330 a of thesemiconductor device 300.

Embodiments of the present invention achieve technical advantages inseveral different multiple gate transistor device applications. Forexample, embodiments of the invention may be implemented in NMOS highperformance (HP) devices, NMOS low operation power (LOP) devices, NMOSlow standby power (LSTP) devices, PMOS high performance devices, PMOSlow operation power devices, and PMOS low standby power devices, asexamples.

Although embodiments of the present invention are described herein beingformed on semiconductor-on-insulator substrates, embodiments of thepresent invention may also be formed on bulk substrates, for example.

Novel semiconductor devices comprising CMOS multiple gate devices havingPMOS and NMOS devices are formed in accordance with embodiments of thepresent invention. Advantages of preferred embodiments of the presentinvention include providing methods of fabricating semiconductor devices100, 200, and 300 and structures thereof. The multiple gate PMOS andNMOS transistors of CMOS devices preferably have a substantiallysymmetric V_(t) that is tunable by adjusting the work function of thetransistors using the novel embodiments of the present inventiondescribed herein. Several means of tuning the work function oftransistors are described herein, by selection and control of thesilicide or germanide phase, doping levels, and/or the selection of thegate dielectric materials, as examples.

Embodiments of the present invention advantageously provide novelmethods and structures for manufacturing parasitic bi-modal free V_(t)behavior FinFET devices 130, 230 a, 230 b, and 330 a that avoid orreduce three-dimensional silicide or germanide phase inhomogeneities ofthe gate electrode materials 122, 222 a, 222 b, and 322 a. A thickerhard mask 110/112/114, 210 a/212 a/214 a, 210 b/212 b/214 b, and 310a/312 a/314 a shifts any silicide or germanide phase inhomogeneities inthe upper corners 126 upwards, and a recessed buried insulating material106, 206, 306 shifts any silicide or germanide phase inhomogeneities inthe lower corners 128 downwards.

Although embodiments of the present invention and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, it will be readily understood by those skilled in the artthat many of the features, functions, processes, and materials describedherein may be varied while remaining within the scope of the presentinvention. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

1. A transistor comprising: a semiconductive fin comprising a channelregion, the fin having a first side, a second side opposite the firstside and a top surface, the fin having a height; a gate dielectricdisposed over the first side, the top surface and the second side; agate electrode disposed over the gate dielectric; and wherein the gateelectrode comprises a silicide or germanide, and wherein the gateelectrode comprises a substantially homogeneous phase of the silicide orgermanide over the height of the fin.
 2. The transistor according toclaim 1, wherein the silicide or germanide comprises undoped NiSi orNi₃Si₂, or NiSi or Ni₃Si₂ doped with P or B.
 3. The transistor accordingto claim 1, wherein the gate dielectric comprise HfO₂, HfSiO_(x), Al₂O₃,ZrO₂, ZrSiO_(x), Ta₂O₅, La₂O₃, HfAlO_(x), ZrAlO_(x), SiAlO_(x),HfSiAlO_(x), ZrSiAlO_(x), Y₂O₃, TiO₂, nitrides thereof, Si_(x)N_(y),SiON, SiO₂, or multiple layers or combinations thereof.
 4. Thetransistor according to claim 1, further comprising an isolation layerdisposed over the top surface of the fin.
 5. The transistor according toclaim 4, wherein the fin is disposed over a buried insulating layer, theburied insulating layer comprising a recess below a bottom surface ofthe fin proximate the fin, and wherein the isolation layer or the recessin the buried insulating layer, or both, comprise a greater thicknessthan the gate electrode.
 6. A CMOS device comprising: a PMOS FinFETcomprising a first semiconductive fin having first sidewalls and a firstheight; a first gate dielectric disposed on the first sidewalls of thefirst fin; and a first gate electrode disposed over the first gatedielectric, wherein the first gate electrode comprises a substantiallyhomogeneous first phase of a first silicide or germanide over the firstheight; and a NMOS FinFET comprising a second semiconductive fin havingsecond sidewalls and a second height; a second gate dielectric disposedon the second sidewalls of the second fin; and a second gate electrodedisposed over the second gate dielectric, wherein the second gateelectrode comprises a substantially homogeneous second phase of a secondsilicide or germanide over the second height.
 7. The CMOS deviceaccording to claim 6, wherein the first phase is different than thesecond phase or wherein the first phase is the same as the second phase.8. The CMOS device according to claim 6, wherein the PMOS FinFET and theNMOS FinFET comprise undoped NiSi or Ni₃Si₂.
 9. The CMOS deviceaccording to claim 6, wherein the PMOS FinFET and the NMOS FinFETcomprise doped NiSi or Ni₃Si₂.
 10. The CMOS device according to claim 6,wherein the PMOS FinFET comprises a work function of about 4.6 to 4.9eV, and wherein the NMOS FinFET comprises a work function of about 4.4to 4.7 eV.
 11. The CMOS device according to claim 6, further comprisinga plurality of the PMOS FinFETs and a plurality of the NMOS FinFETs. 12.A transistor comprising: a semiconductive fin having sidewalls and aheight; a gate dielectric disposed on the sidewalls of the fin; and agate electrode disposed over the gate dielectric, wherein the gateelectrode comprises a substantially homogeneous second phase of a secondsilicide or germanide over the height.
 13. The transistor according toclaim 12, further comprising an isolation layer over a top surface ofthe fin, the isolation layer.
 14. The transistor according to claim 13,wherein the isolation layer comprises three layers, wherein a firstlayer comprise a first oxide, wherein a second layer comprises anitride, and wherein a third layer comprises second oxide.
 15. Thetransistor according to claim 13, wherein the isolation layer comprise agreater thickness than the gate electrode.
 16. The transistor accordingto claim 12, wherein the fin is disposed over a buried insulating layer,the buried insulating layer comprising a recess below a bottom surfaceof the fin proximate the fin.
 17. The transistor according to claim 16,wherein the recess in the buried insulating layer comprises a greaterthickness than the gate electrode.
 18. The transistor according to claim12, wherein the gate electrode is a FUSI.
 19. The transistor accordingto claim 12, wherein the fin comprises silicon or a compoundsemiconductor such as GaAs, InP, Si/Ge or SiC.
 20. The transistoraccording to claim 12, wherein the transistor comprises aheight-to-width aspect ratio of about 3:1 or less.